We are developing a system for a computer-aided study of phenotypic heterogeneity of diploid cells in tissue culture. Features such as cell velocity, morphology, size, cytostructure, interdivision time, social behavior, and cell death are followed in clonal progressions started at various stages in the life of normal diploid human cell strains. The computer will be used to gather data from 16-mm tape lapse films of clones, as well as to perform statistical time-series analysis on the data. Our investigation centers around the problem of aging in mammalian cell strains. The question is asked whether cells which have left cell cycle show altered structural, biochemical, or physiological properties. The basic method of approach is to film a cell lineage starting with a single cell and to follow it through 7-10 generations using time lapse cinematography. We wish to know whether departure from cell cycle can be correlated with changes in cytostructural organization, with response to mitogenic hormones, with distribution and amount of particular contractile proteins, and with other biochemical characteristics. Since some cells of all population doubling levels (PDL) appear to leave cycle permanently, we ask whether cells of different PDLs which do, are phenotypically similar. Since the history of all cells in a clone is recorded it is possible to carry out a variety of tests when the clonal progression is terminated which give information about individual cells. For example, we can correlate in glycerinated cells contraction, or absence of it, with length of time out of cycle and with the number of divisions through which a cell has passed. We are focusing on the question of whether departure from cell cycle can be taken necessarily as a sign of aging.